1. Technical Field
The present invention generally relates to a display device and a test probe for testing the display device. More particularly, the invention relates to a display device that is provided with a light detection unit that detects the intensity of ambient light and is capable of automatically controlling the luminosity of an illumination unit and/or the luminosity of the display device on the basis of the intensity of ambient light detected by the light detection unit. Moreover, the display device to which the invention is directed makes it possible to easily conduct a test on light-sensor characteristics. The invention further relates to a test probe for testing such a display device.
2. Related Art
These days, various kinds of display devices such as a liquid crystal display device, an organic electroluminescence (EL) display device, a plasma display device, and the like are widely used. In some cases, an image displayed by a display device is difficult to view depending on the luminous intensity level of external light (i.e., ambient light). As a means for providing a solution to such a problem, it is known in the art to provide a light detection unit such as a light sensor as a component of a display device. For example, when a light sensor is provided in a liquid crystal display panel, the luminosity of a backlight, a sidelight, a front light, or the like is controlled depending on the detection output of the light sensor. When a light sensor is provided in other display devices, the light emission brightness level of a display image is controlled depending on the detection output of the light sensor.
As an example of such a sensor-based control technique, an invention of a liquid crystal display device that automatically turns a backlight or the like ON/OFF depending on ambient luminosity conditions is described in JP-A-2002-131719. Specifically, in the configuration of a liquid crystal display device described in JP-A-2002-131719, a light sensor that is made up of thin film transistors (TFT), which might be hereafter referred to as “TFT light sensor”, is formed over a substrate of a liquid crystal display panel. The liquid crystal display device described in JP-A-2002-131719 detects the optical leakage current of the TFT light sensor so as to automatically turn the backlight into an ON/OFF state depending on ambient luminosity conditions. As another example of such a sensor-based control technique, an invention of a liquid crystal display device that is provided with a TFT light sensor for external light illumination detection and a TFT light sensor for backlight illumination detection, both of which are formed over a substrate of a liquid crystal display panel, is described in JP-A-2000-122575. The liquid crystal display device described in JP-A-2000-122575 controls a backlight or the like on the basis of the detection result of both TFT light sensors. The liquid crystal display device described in JP-A-2002-131719 or JP-A-2000-122575 is capable of automatically controlling the luminosity of a backlight or the like depending on the luminosity of external light on the basis of the output of the TFT light sensor/sensors. Therefore, it is possible for a user to visually observe a display image without any difficulty even when the luminosity of external light changes.
In the configuration of a display device of the related art, a light sensor is provided at, for example, a peripheral area that surrounds a display area of the display device. A wiring pattern is formed at the peripheral area for providing electric connection to the light sensor. The light-sensor connection lines, which are formed at the peripheral area for providing electric connection to the light sensor, are routed at an area that is not the same as an area at which driving lines are formed for, for example, driving liquid crystal or for other display driving operation because input/output signals that are sent over the lines that are formed for providing electric connection to the light sensor are completely different from input/output signals that are sent over the lines that are formed for driving operation. Although the lines that are formed for providing electric connection to the light sensor are routed at an area different from an area at which the lines for driving operation are formed, it is necessary to conduct an in-process wiring test not only for the lines that are formed for driving operation but also for the lines that are formed for providing electric connection to the light sensor because there is a possibility of a wiring defect such as a broken wire, a short circuit with other adjacent line, and the like.
An invention of a display device that has a function of detecting a possible wiring defect in lines that are formed for driving operation, lines that are formed for providing electric connection to a light sensor, and the like is described in JP-A-2008-9246. A display device that is described in JP-A-2008-9246 is provided with at least one switching element that provides electric connection between at least one of a plurality of signal lines and at least one photo sensor element. A video voltage is applied to a plurality of pixels through the signal lines. The switching element is turned ON at the time of testing. By this means, a test is conducted to detect any defect in the photo sensor element and photo sensor wiring depending on the lighting state of a display panel at the time when a predetermined testing voltage is applied to the photo sensor element via the photo sensor wiring. On the other hand, the switching element is turned OFF at the time of normal use so as to make the pixels and the photo sensor independent of each other.
The display device that is disclosed in JP-A-2008-9246 explained above offers an advantageous effect in that it is possible to conduct an in-process test to detect a possible display defect in the display panel and a possible sensor defect in the photo sensor separately. However, generally speaking, defects in a display panel and a light sensor includes, in addition to a short circuit defect that causes low resistance, a short circuit at a high resistance of a few tens of kilo ohms (kΩ) or greater (hereafter may be referred to as “high resistance short”). In this respect, the display device that is disclosed in JP-A-2008-9246 explained above has the following problem that remains to be solved. Since the voltage of the signal line hardly changes in a case where there is a high resistance short of a few tens of kilo ohms or greater between the electrodes of the light sensor, it is difficult to detect a defect in the light-sensing element on the basis of the differences in the lighting condition of the pixels. That is, the display device that is disclosed in JP-A-2008-9246 explained above makes it possible to detect a low resistance short only.
In order to detect a high resistance short of a light sensor, it is necessary to develop a method that makes it possible to detect a very small value of an electric current that flows between testing terminals. In addition, it is demanded to develop a testing scheme that makes it possible to conduct both a lighting test and a light-sensor test without changing a conventionally used test probe and conventionally used test facilities. An example of a conventional means for testing a display device with the use of a test probe easily is described in JP-A-2006-243706.